This invention concerns coal liquefaction. More particularly, it concerns a process for treating coal with hydrogen, in the absence of any added catalyst and/or solvent, to obtain a high yield of coal tars. The utility of the invention resides in the production of high yields of desirable long chain aromatic hydrocarbons from coal.
Processes for treating coal with hydrogen have been known for many years. Prior art references include U.S. Pat. No. 2,658,861; 2,832,724; 3,030,297; and 3,152,063. Typically, these processes have mixed crushed coal with various solvents, with or without added catalyst, and have heated the mixture to reaction temperature, for an extended period of time, in the presence or absence of hydrogen. Such processes have generally given a wide range of products, from gases to light hydrocarbons to high-boiling liquids, in addition to the solid residues. For example, U.S. Pat. No. 3,823,084, issued to W. C. Schroeder on July 9, 1974 discloses mixing coal and hydrogen, in the absence of a solvent, passing the mixture through a bed of hydrogenation catalyst, and recovering liquid and gaseous hydrocarbon products from the product stream. The disadvantages of such processes include addition of a catalyst that will survive the severe reaction conditions, removal of the catalyst from the effluent stream, recovery of a broad spectrum of gaseous, low-boiling and high-boiling liquids, the necessity for solvent addition and removal, and additional processing steps to separate, remove and recycle various portions of the reaction stream.